This work entails investigation of the role of lysosomes in protein turnover and the uptake of marker macromolecules into the lysosomal system and their disposition. In addition we are investigating the chemical composition and the regulation of synthesis of a peptide we have isolated from liver which modulates the degradation of hepatic phosphofructokinase. BIBLIOGRAPHIC REFERENCES: "Regulation of Protein Turnover and the Role of Lysosomes", H. L. Segal, G. A. Dunaway, Jr., and J. R. Winkler, in "Metabolic Interconversion of Enzymes - 1975", S. Shaltiel, ed., Springer-Verlag, Berlin, 1976, in press. "Mechanism and Regulation of Protein Turnover". H. L. Segal, in "Current Topics in Cellular Regulation", B. L. Horecker and E. R. Stadtman, eds., vol. 11, Academic Press, New York, 1976, in press.